The National Railway Network, like in many other European and extra-European countries, is well developed in the territory in a capillary way. Our territory has a particularly varied distribution of mountain ranges, which has caused the construction of numerous bridges and viaducts.
Among the most frequent types of bridges there are arch bridges (see FIG. 1), with one or more spans, generally masonry bridges or bridges of reinforced concrete, and those with decks are made with a mixed structure of steel and concrete, that is of reinforced concrete. The drawings do not report bridges with decks, however, the considerations made in relation to the arch bridges are valid also for the bridges with decks, if not otherwise specified.
Although many of the actually used bridges were built and operated many years ago (many of them date back to before the second world war), they are kept in static conditions sufficient to ensure the safety of trains passing on them, in spite of the present railway traffic.